採用dom實現複選框全選、取消效果

<form action="">
    愛好：<br/>
    <input type="checkbox" id="all">全選<br/>
    <input type="checkbox"  name="hobby" value="唱歌">唱歌
    <input type="checkbox"  name="hobby" value="跳舞">跳舞
    <input type="checkbox"  name="hobby" value="學習">學習
    <input type="checkbox"  name="hobby" value="玩耍">玩耍<br/>
    <button id="choice" value="選擇">選擇</button>
</form>

<script>
window.onload = function(){
    document.getElementById("all").addEventListener("click",function(){
        var a = document.getElementById("all");
        var b = document.getElementsByName("hobby");
        for(var i=0;i< b.length;i++) {
            b[i].checked = a.checked;
        }
    },false)
}

</script>